COMPOSITION AND CHARACTERS OF URINE 1247 



carried to the liver, where it undergoes dehydration with the produc- 

 tion of urea. Its amount will therefore be directly proportional to 

 the amount of protein taken as food. A smaller proportion is derived 

 from the breakdown of the tissues of the body. This endogenous 

 moiety may undergo considerable increase under any conditions which 

 cause a rapid disintegration of the tissues. Thus there is a large rise 

 in the urea output, even in a starving individual, in febrile conditions. 



In order to prepare urea from urine advantage may be taken of the insolu- 

 bility of its combination with nitric acid. Urine is concentrated to about one- 

 sixth of its bulk. It is then cooled and treated with twice its volume of pure 

 concentrated nitric acid, care being taken to keep the whole mixture cool. Urea 

 nitrate is precipitated. The precipitate is collected, dried roughly by pressing 

 between filter paper, and then rubbed up with fresh barium carbonate. Barium 

 nitrate is formed and urea set free. The whole mass is dried and treated with 

 hot absolute alcohol, in which the barium nitrate is insoluble. On filtering off 

 the barium nitrate a pure solution of urea is obtained from which the urea will 

 crystallise on allowing the alcohol to evaporate. 



CREATININE. Creatinine is a normal constituent of urine, in 

 which it occurs in quantities of O8 to 1-3 grm. in the twenty-four hours. 

 It is easily produced from creatine by boiling the latter with strong 

 hydrochloric acid, when a process of dehydration occurs. Creatine 

 has the formula : 



NH 2 



NH = = C N(CH 3 )CH 2 .COOH. 

 On dehydration it is converted into creatinine : 



NH 



NH == C N(CH 3 )CH 2 CO 



Creatinine may be obtained from urine in the following way. The urine is 

 made alkaline with milk of lime and treated with calcium chloride and filtered. 

 The filtrate is slightly acidified with acetic acid and evaporated on the water 

 bath to a syrupy consistence. A little sodium acetate is added and the mixture 

 extracted with alcohol. The filtered alcoholic extract is now treated with a 

 concentrated neutral alcoholic solution of zinc chloride. A crystalline precipitate 

 of creatinine zinc chloride is produced. After two days this precipitate is collected 

 on a filter, washed with alcohol, dissolved in water, and then boiled for a quarter 

 of an hour with lead hydrate. The mixture is then filtered and the filtrate evapo- 

 rated to dryness. The dry residue is now extracted with cold alcohol and filtered. 

 On allowing the alcohol to evaporate, crystals of creatinine separate out (Fig. 

 516). It gives the following tests : 



(1) WEYL'S TEST. On treating a solution of creatinine with a small quan- 

 tity of very dilute sodium nitroprusside solution and then with weak caustic 

 alkali, a rich ruby-red colour is produced which gradually changes to yellow. 

 On now adding acetic acid and warming, the solution becomes green and then 

 blue, and finally a precipitate of Prussian blue is formed. 



(2) JAFFE'S TEST. On treating a solution of creatinine with a few drops 

 of a watery solution of picric acid and dilute caustic potash, an intense red 



